Microgravity Science and Technology最新文献

We investigate the linear stability of an incompressible, viscous liquid thin film placed on a solid substrate subjected to vertical harmonic vibrations in the presence of gravity and a negative temperature gradient. The substrate oscillates with a finite frequency, compared to the viscous time and large amplitude, compared to the film thickness. By separating the governing equations into oscillatory (fast) and time-averaged (slow) components, we obtain an analytical solution for the oscillatory fields and represent their velocity structure through isolines of stream function. Averaging over the fast time scale yields a set of amplitude equations that describe the slow evolution of the free deformable surface. The stability analysis reveals that gravity and surface tension stabilise the interface, while van der Waals attraction and the imposed thermal gradient destabilise. Vertical vibrations may stabilise the surface: at low frequencies even large amplitudes fail to suppress the long-wave instability for moderate and high Marangoni numbers, whereas at moderate to high frequencies sufficiently strong vibrations stabilise the film across the entire wavenumber spectrum. For a huge values of Marangoni number small vibrations are ineffective, but when Marangoni number is small complete stabilisation is achieved at moderate frequencies for all amplitudes considered. Results obtained in limiting cases are consistent with the previous studies for isothermal and non-vibrated cases.

The study numerically investigates the mass transfer in an inclined two-layer porous channel in the gravitational field. The lower region of the channel is occupied by a porous medium, while the upper region consists of a pure fluid. The initial concentration distribution is such that the impurity is localized in the central part of the porous domain. The upper and lower walls of the channel are solid and no-flux boundary condition for the concentration is applied. Periodic boundary conditions are applied for the velocity field on the side walls, and the flow is driven by the longitudinal component of the velocity induced by the gravitational field and channel inclination. For the concentration field two boundary condition types are examined on the side walls: periodic boundary conditions, and a non-periodic characterized by a vanishing concentration at the left wall and a constant flux condition at the right wall. The problem is solved for constant porosity and permeability coefficients, with the Schmidt number fixed at (varvec{Sc = 10^3 }). The study focuses on the diffusion of an impurity into a viscous pure fluid for various Darcy numbers (varvec{Da}). The simulations are conducted using the Lattice Boltzmann Method (LBM) on a D2Q9 lattice. A modified multiple relaxation-time (MRT) LBM scheme was introduced for the mass transfer simulation in porous media. The effectiveness and applicability of the proposed scheme for such classes of problems are substantiated through the presented results. For the periodic boundary conditions, it is shown that the integral concentration within the domain is conserved, and the concentration profiles both inside and outside the porous layer converge toward the average value. In contrast, under non-periodic boundary conditions, the impurity is gradually washed out of the domain. The obtained numerical results also demonstrate that the type of boundary condition imposed on the concentration field at the side walls has a negligible effect on the velocity field. At a higher Darcy number (varvec{Da = 10^{-2} }), the evolution of the impurity is more pronounced, and the system reaches a steady state more rapidly. For lower Darcy numbers ((varvec{ Da = 10^{-3} }) and (varvec{Da = 10^{-4}})), the impurity evolution rate outside the porous matrix is approximately the same, whereas within the porous matrix, the evolution is more intense for larger Darcy numbers.

To address issues in the construction of the ground test platform and closed-loop control performance evaluation of the drag-free system in space gravitational wave detection, this paper proposes a verification method based on a ground composite semi-physical drag-free simulation system. A ground simulator for drag-free simulation is innovatively designed based on the configuration of a drag-free satellite with two test masses. The scaling laws between the space prototype and the ground simulator are determined by using the Pi theorem. The scaling laws are used as the design guide for the ground simulator. According to the principle of the drag-free satellite in the science mode, the drag-free controller is designed using the active disturbance rejection control (ADRC) algorithm, and the control scaling laws are established for the controller design of the ground simulator. The closed-loop similarity of the two systems is studied, and the simulation results indicate that the two systems exhibit similar closed-loop dynamic behavior. The drag-free controller of the space prototype can be transferred to the ground simulator for verification using control scaling laws.

Mean flows induced by linear high frequency vibrations of a solid body immersed in a liquid or in contact with a free surface are studied experimentally and theoretically. It is shown that the flow structure and intensity strongly depend on a liquid viscosity and the shape of a solid body. Experiments and numerical simulations performed for the configuration imitating the Czochralski crystal growth method enabled us to emphasize the role of different vibrational mechanisms, and the role of the radius of curvature of a crystal edge (in the case of crystal immersed in the melt). Three different vibrational mechanisms of mean flow generation have been identified and emphasized.

The work is devoted to an experimental study of the dynamics of a light sphere rising in a vertical rotating cylinder filled with fluid. In a rapidly rotating cylinder, the fluid flow is two-dimensional and has a complex multilayer structure. A Taylor-Proudman column forms around the sphere and rotates at an angular velocity that differs from that of the surrounding fluid. The axial motion of the fluid occurs exclusively within the Stewartson shear layer, located at the boundary of the Taylor-Proudman column. In contrast, the motion in the radial direction is attributed to the Ekman shear layer, which is located at the end-walls of the cylinder. Consequently, a rising sphere experiences a greater drag force compared to the case where rotation is absent. The effect of the cylinder height on the sphere velocity in a low-viscosity fluid is experimentally studied. Theoretical predictions indicate that the sphere velocity decreases with decreasing cylinder height, a finding that is corroborated by the present study. It is shown that the velocity of the sphere decreases in accordance with a power law as the rotation rate of the cylinder increases. It appears that the axial velocity is determined by the Ekman number for all cylinder heights that have been investigated.

In this study, we investigated the backdraft phenomenon numerically under different gravity conditions and 4 openings using the Fire Dynamics Simulator (FDS) code. Four different opening geometries are studied under ten different gravity conditions. The rate at which oxygen reaches an ignition block in the enclosure in the presence of gravity currents plays an important role in the onset of ignition, the subsequent backdraft formation, and the maximum pressure built inside the enclosure before the onset of backdraft. This role also explains why these effects are different under different openings. We observe that the gravity strength affects the ignition time and the onset of backdraft non-linearly. Moreover, it is found that the smoke exiting the enclosure cannot be considered a reliable precursor for the onset of backdraft to allow people on the outside to undertake necessary precautions. The effect of backdraft in the form of heat flow and impact force at the exit is also studied. It is found that the effect of heat flow is more severe than that of the impact force.

The mechanism controlling the soot process of a laminar jet diffusion flame is investigated through experiments and theoretical analyses. The effect of hydrodynamic characteristics on the soot volume fraction and smoke point of jet flames is focused on. The luminous flame height at smoke point under normal gravity and microgravity environment were compared. The soot concentration and temperature distributions of laminar ethylene diffusion flames with different co-flow air velocities and fuel nozzle diameters are measured by light extinction method and RGB two-color pyrometry method, respectively. High co-flow air velocity and small nozzle diameter can reduce the soot content in the flame, resulting in a higher smoke point, which is related to the increase in flame temperature caused by a shorter residence time and better fuel–air mixing conditions. The simple prediction of the theoretical oxidation zone shows that decreasing the nozzle diameter may make the oxidation zone longer, favouring the oxidation of soot in the flame tip region. Furthermore, a brief theoretical analysis of the contributions of fuel exit momentum and buoyancy in residence time during fuel combustion is presented. It is considered that when the fuel outlet diameter is small, the nozzle diameter may affect the residence time and hence the smoke point to a greater extent. This work provides new insights into the influence of hydrodynamics on soot process in laminar jet diffusion flame.

Nitrification supports long-term human stays in space by converting urine-derived ammonia into harmless nitrate, which aids in crop production. In space, oxygen availability is often limited due to the constraints of closed life support systems and need for strict resource management. In this study, we aimed to investigate the effects of simulated microgravity (SMG) on the activities of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in nitrifying sludge under oxygen-limited conditions. Notably, no difference in AOB activity was observed between the normal gravity (NG; 1.92 ± 0.27 mg-N g-VSS⁻¹ h⁻¹) and SMG (2.08 ± 0.33 mg-N g-VSS⁻¹ h⁻¹) conditions. In contrast, NOB activity was significantly elevated under SMG condition (1.79 ± 0.09 mg-N g-VSS⁻¹ h⁻¹) compared to that under NG condition (0.83 ± 0.08 mg-N g-VSS⁻¹ h⁻¹). Oxygen balance analysis revealed competition for available oxygen between NOB and other aerobic bacteria under NG; however, this competition was mitigated under SMG. Gravity-dependent convection caused a high buoyant plume velocity of 8.6 × 10⁻³ cm s⁻¹ under NG, indicating nitrite diffused within the AOB- and NOB-containing flocs. However, this convection was suppressed under SMG, resulting in a decreased plum velocity of 2.7 × 10⁻⁴ cm s⁻¹, indicating that nitrite accumulated around the flocs, enhancing the nitrite-to-nitrate metabolism. To the best of our knowledge, this study is the first to quantitatively evaluate the effect of microgravity on the activity of nitrifying sludge under oxygen-limited conditions and outline the potential mechanism by which NOB activity is maintained at a higher level under microgravity than under terrestrial gravity.

Surface tension tanks are the most widely used propellant storage systems in spacecraft and primarily rely on liquid surface tension for propellant delivery and gas–liquid separation. This study focuses on the orientation and reorientation processes of propellants in a partial-controlled vane-type tank under different microgravity accelerations. The distribution of the propellant in the tank was simulated, and the results were compared with the drop tower test results. Considering the joint action of the vertical vanes and accumulator, the propellant transport performance, free liquid surface shape, and centroid distribution of the tank under different liquid filling volumes were analyzed. The results indicate that during propellant orientation, the free surface undergoes a transition from a wave-like shape to a U-shape, ultimately converging at the top end of the tank to encapsulate the gas into a pocket. Higher tank fill levels correlated with an increased propellant delivery volume and greater centroid offset. The accumulator functions to retain liquid and prevent gas ingress, thereby enabling gas–liquid separation, but does not possess active gas venting capabilities. Under extreme operational conditions, the partial-controlled system's functionality may be constrained by insufficient propellant fill/residual levels. This study provides a comprehensive investigation of propellant management processes in partial-controlled vane-type tanks and offers guidance for further optimization of vane-type propellant management devices.

We analyze the sensitivity to image defects of the processing algorithm proposed by Salgado Sánchez et al. (Microgravity Sci. Technol. 37, 12, 2025) to evaluate melting bridge experiments in the context of the MarPCM microgravity project (Porter et al., Acta Astronaut. 210, 212–223, 2023). The algorithm uses the projection of input images onto the first m singular vectors (modes), obtained via Singular Value Decomposition (SVD), of the original (non-defective) image database. The resulting set of m amplitudes is then used as input for an Artificial Neural Network (ANN) that is trained to give the corresponding liquid fraction as an output. For the analysis presented here, the images are modified to generate a new database that includes rotated images, which represent optical misalignment, overexposed and underexposed images, which represent incorrect exposure time and/or aperture settings in the camera, noisy images and gappy images, which model the presence of dead pixels, bubbles and large reflections that compromise certain regions of the image. The results suggest that only relatively large defects are a concern for processing the experiment and that the most critical case is that of gappy images. Data repair algorithms based on SVD can be used to correct the defective images and reconstruct the missing information, which then allows for accurate processing.